1. Field of the Invention
The present invention relates to an optically compensatory polarizer for use in forming a liquid-crystal display device excellent in contrast and easy to view with a wide viewing angle but without being discolored.
2. Description of the Related Art
An optically compensatory polarizer has been heretofore known (“Improvement of Polarizer and Retardation Film for LCDs”, Display and Imaging, 1993, Vol. 1, pp.257-264). The optically compensatory polarizer is produced as follows. Iodine or a dichromatic substance such as dichromatic dye is adsorbed to a polyvinyl alcohol film. The film is then drawn. Protective layers of triacetyl cellulose or the like are provided on opposite surfaces of the film to thereby prepare a polarizer. An optically compensating film having birefringence is laminated on the polarizer to thereby complete the production of the optically compensatory polarizer. When two optically compensatory polarizers produced in such a manner are arranged in the form of crossed-Nicol, it is possible to prevent light leakage at a wide viewing angle.
That is, even in the case where light transmission in a direction of a line normal to each of polarizers arranged in the form of crossed-Nicol is suppressed to achieve transmittance of about 0% between the polarizers, there is still a problem that gradual increase of light leakage with increase of the oblique viewing angle may make it impossible to achieve such transmittance of 0% because the apparent angle of an axis is out of perpendicularity when viewing is made from an oblique direction at an azimuth shifted from a direction of an optical axis. The arrangement of such polarizers in the form of crossed-Nicol is a method for achieving black display in a liquid-crystal display device. However, when viewing is made in an oblique direction, use of such polarizers in a liquid-crystal display device causes reduction of contrast to thereby result in reduction in visibility. Optically compensatory polarizers are therefore provided to prevent such light leakage. The background-art optically compensatory polarizer, however, has a problem that light transmitted through the optically compensatory polarizer is discolored.